1. Field of the Invention
The present invention relates to conveyors and, more particularly, relates to a method and apparatus for detecting misalignment of a conveyor.
2. Discussion of the Related Art
A conveyor belt assembly typically comprises a plurality of pulleys, at least one of which is powered, that is mounted onto a frame, and an elastic material (or conveyor belt) that is wrapped around the pulleys. In the event that the conveyor belt assembly is being used to transport the load over long distances, additional support pulleys or rollers may be placed underneath the conveyor belt. The conveyor belt becomes operational when the pulleys rotate, thereby moving the conveyor belt forward.
In order to ensure that the force of the pulley will be sufficient to drive the conveyor belt, the conveyor belt is placed under tension so that friction between the conveyor belt and the drive pulley is sufficient to ensure that the conveyor belt does not slip against the surface of the pulley. The typical conveyor belt is therefore of an elastic material, such as a reinforced rubber composite. However, uneven loading of the belt, belt material inhomogeneity, and unequal temperature distribution across the belt can cause the belt to stretch unevenly, thereby causing the belt to slide laterally with respect to the pulleys and become misaligned during use, resulting in damaged belt edges and a shorter belt life. A misaligned belt could also, in some situations, damage the load.
Devices have been implemented in the past to detect a misaligned conveyor belt. One such device comprises a bronze disc that is placed adjacent at least one side of the belt such that, when the belt becomes misaligned, it rubs against the disc, thereby generating heat that is conducted through the disc. A thermocouple embedded in the disc measures the heat and outputs voltage signals to a programmable controller that processes the signals to measure the temperature. A threshold temperature is programmed into a human machine interface and communicated to the controller via an analog circuit such that, when the measured temperature exceeds the threshold temperature, the controller activates an alarm signal that is detectable by a user.
Several disadvantages are associated with this device. First, the output of this device requires a long response time in detecting the misalignment of the conveyor belt. Specifically, a significant amount of time elapses while frictional forces between the belt and disc generate heat and while the generated heat is conducted through the bronze disc to the thermocouple. During this delay, the conveyor belt may become increasingly misaligned. Additionally, no back-up sensors exist on this device to allow a user stationed at a location remote from a conveyor belt to make a reliable determination that the belt has become misaligned. For example, the user may be unsure that the temperature sensor is functioning properly. Finally, in order to test the operability of the sensor, the bronze disc must be manually heated until the measured temperature exceeds the threshold temperature. This process is cumbersome and inefficient.
The need has therefore arisen to provide a method and apparatus for detecting a misaligned conveyor belt with a quick response time that incorporates back-up features, and allows a user to easily perform diagnostics to ensure the operability of the detection apparatus.